This invention relates to polymerization processes. More particularly, it relates to such processes in which polymerization of methacrylate or acrylate monomers on vent surfaces is inhibited.
Many patents disclose inhibitor paints on the inside surfaces of polymerization reactor vessels for the prevention of formation of scale which could fleck off into the polymer and cause fish-eyes in paint made from the polymer. It is important not to prevent polymerization in the reactor as a whole, but just at the wall surfaces. It would be counterproductive to turn off or slow down polymerization, but the surfaces do need to be inhibited.
Belgian patent 845,168 of 1976 to Schinetzu discloses coating the inside of a polymerization reactor with an organic electron donor and an acceptor and an oxidizing agent or alternatives. As the donors, thiazines are mentioned, and thiophenols are mentioned among the alternatives to oxidizing agents. The result is to permit polymerization in the reactor but to prevent scale formation on the walls.
European patent 172,427 A of 1986 also to Schinetzu, uses compounds that may include 2-amino-4-phenylthiazole or 2-amino-5-phenylthiazole, optionally along with inorganics such as silicates, for the same purpose in vinyl chloride polymerization reactors.
European patent 19,197 of 1980 to Hoechst uses water-soluble substituted thiazine dye salt derivatives of a particular formula for similar purposes in vinyl chloride polymerization equipment.
In vents and conduits where complete elimination of polymerization is desirable, prior practice often used vapor phase inhibitors dissolved in solvents and sprayed into the vents. The high cost of continuous addition and the need to separate the inhibitors and solvents from the products in the case of conduit and reactor use are undesirable features. Also, solvent evaporation can create environmental problems.
If solid inhibitors are applied similarly, incomplete coverage and pluggage possibilities are problems.